FIG. 1 shows a conventional electroluminescent device 100 having one or more organic light emitting (OLED) cells. An OLED cell includes a functional stack of one or more organic functional layers 110 between a transparent conductive layer 105 (e.g., indium tin oxide or ITO) and a conductive layer 115. The conductive layers serve as electrodes. The cells are fabricated on the substrate. The cells can be configured as desired to form a display or lamp. A metallization layer can be formed over the first conductive layer to form interconnections to the electrodes and bond pads 150. The bond pads are coupled to, for example, driving circuitry to control the operation of the OLED cells. A cap 160, which forms a cavity 145, encapsulates the device, hermetically sealing the OLED cells to protect them from the environment (e.g., moisture and/or air.)
In operation, charge carriers are injected through the electrodes for recombination in the functional layers. The recombination of the charge carriers causes the functional layer of the cells to emit visible radiation.
Techniques for depositing polymers include, for example, spin-coating or doctor blading. Such techniques coat the entire substrate surface. Since polymer materials are very soft and partially hygroscopic, they need to be completely removed from the area where the cap is bonded (e.g., cap bonding area) to the substrate. Furthermore, since bond pads are typically formed prior to the deposition of polymer materials, they need to be removed from above the bond pads in order to expose them for coupling to the driving circuitry.
However, limited techniques are available for patterning polymer materials. This is because most techniques which require chemistry (dry or wet) are incompatible with the sensitive polymer materials. A commonly used patterning technique is laser ablation. When laser ablation is used, high laser intensities and long irradiation times are required to remove the polymer materials from selected areas of the substrate. High laser intensities and long irradiation times can damage the metallization or ITO layer beneath the polymers, adversely affecting the device. Moreover, laser ablation may not be able to completely remove the polymer materials since optical absorption decreases as the layer becomes thinner. Incomplete removal of polymer materials from the cap bonding area can result in defective encapsulation, causing failures.
As evidenced from the above discussion, it is desirable to provide an electroluminescent device with reliable encapsulation.